Fosi Audio’s first ever IEMs are open-back for audiophiles

Fosi's impressive, affordable Hi-Fi range now includes these good-looking IEMs

Promotional image of the Fosi Audio IM4 IEMs on a black background showing the two different colour options
(Image credit: Fosi Audio)
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Quick Summary

Fosi Audio is expanding its affordable Hi-Fi range with the introduction of its first ever IEMs. The IM4 buds are made of aluminium alloy, with 10mm dynamic drivers and an open-back design.

Remarkably for their tech, they are currently priced at £59 / $79 / €68.

Fosi Audio is expanding into another sector of the Hi-Fi market: headphones. And like its headphone amps and turntable, the goal is to deliver high-end specs without a sky-high price.

The Fosi Audio IM4 IEMs are its first in-ear monitors (IEMs) and are currently available to preorder on Kickstarter with a price in Hong Kong dollars that works out at roughly £59 / $79 / €68 / AU$119. That's an early bird discount, but the full price is still-low at £82 / $99 / €85 / AU$149.

These IEMs are open-backed, which is relatively uncommon among rivals in this price bracket. The upside is the promise of a wider, more natural sound stage and the downside is more dirty looks if you're listening loud on the bus.

Promotional image of the Fosi Audio IM4 IEMs on a black background showing the three different kinds of ear tips provided

(Image credit: Fosi Audio)

Fosi Audio IM4: key features

The IM4 IEMs are made from CNC-machined aluminium alloy and each ear gets a single, dual-magnet 10mm dynamic driver with a PU beryllium-plated diaphragm. This, Fosi says, delivers low distortion, great detail and "a balanced, fatigue-free sound". They also feature "sparkling" treble and tight bass.

Fosi says that its tuning means that the single-driver setup performs just as well as rival multi-driver designs. The rear of the inner chamber is sound-damped to eliminate harshness and resonance peaks and the tuning features a "subtle treble lift".

The two-pin cable is braided with 4 strands of 392-core 5N high-purity OFC silver-plated wire and features a gold-plated connector. And including that cable, the total weight is just 38g, with each IEM weighing a mere 7g.

The package includes two sets of nozzles: aluminium and brass. And there are three sizes of ear tips in three different flavours: balanced, bass and deep bass.

The Fosi Audio IM4 are available to preorder now for shipping in November 2025.

Carrie Marshall
Carrie Marshall

Writer, musician and broadcaster Carrie Marshall has been covering technology since 1998 and is particularly interested in how tech can help us live our best lives. Her CV is a who’s who of magazines, newspapers, websites and radio programmes ranging from T3, Techradar and MacFormat to the BBC, Sunday Post and People’s Friend. Carrie has written more than a dozen books, ghost-wrote two more and co-wrote seven more books and a Radio 2 documentary series; her memoir, Carrie Kills A Man, was shortlisted for the British Book Awards. When she’s not scribbling, Carrie is the singer in Glaswegian rock band Unquiet Mind (unquietmindmusic).

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